Manufacture of metallic filaments for electric incandescent lamps.



In-21.111181 S0 as to IEOI'IIl 133W filaments.

UNITED STAWENT OFFICE.

JAMES ALEXANDER scon'LAR, or HAMMERSMITH, LONDON, ENGLAND, Assmnon'romcx, KERR & COMPANY, LIMITED, or LONDON, ENGLAND.

MANUFACTURE OF METALLIC FILAMENTS FOR ELECTRIC INCAIVDESC ENT LAMPS.

No Drawing.

To all whom it may concern:

Be it known that I, JAMES ALEXANDER ScoUmn, a subject of the King ofEngland,

residing in Hammersmith, London, Eng-.

culties in manufacture and the disadvantages of finished metallicfilaments have arisen from the binding agent. 1

The raw material which we employ is tungsten in the form of a. Very finepowder, which may be obtained for example by the reduction of the oxidat a high temperature with-hydrogen or with zinc. I The finely powderedmetal which We employ is preferably as pure aspossible, and it isespeclally desirable to avoid the presence therein of any considerablepercentage of oxid or hydroxid, since the presence of these or otherimpurities may prevent the production of good filaments. Satisfactoryresults have, however, been obtained with tungsten powder having anoxygen absorption of 24.8 to 25.3 per cent-., and a simple test sufiicesto show whether anygiven sample can be successfully used in the process.According to this invention the'tungsten powder is mixed with a smallproportion of sodium silicate solution'in the thick gelatinous orviscous form, the mixing being carried out in such a way as to effect auniform incorporation of the powder with the binding agent. Theresulting mass or paste is squirted through dies in any well-known Thesefilaments are then-subjected to heat so as to render them conductive andto cause them to sinter into finished metallic filaments. During thisprocess the silicate is substantially eliminated. For example, thesquirted filaments may be dried, then baked by the application ofexternal heat, and finally sin- Specification of Letters Patent.

\ Patented July 21, 1914.

Application filed March 14, 1913. Serial No. 754,346.

tered by passing a current through them in an inert atmosphere so as toraise them to an intense white heatQ Instead of baking and sintering thefilaments separately, the raw squirted filaments may be subjected toheat in a suitable inert atmosphere so as both to render them conductiveand to sinter them in oneoperation. The best proportion of sodiumsilicate solution to employ varies to some extent with the physical andchemical qualities of the tungsten powder, the thickness of filamentrequired, and other circumstances; but it should in any case be small,and an excess should be avoided. In most cases" I have found the bestresults to be obtained on using the proportion stated in the followingex ample which. is one method of producing tungsten filaments accordingto this invention with separate baking and sintering operations Onehundred and twenty (120) grams of ing operation a few drops of water areadded if necessary. Thereafter the mass .is squirted through a die, thefilament on issuing from the press being passed through a hotatmosphere, and collected on cards or trays.

The filaments are next dried and .then in-' troduced in suitablereceptacles (say trays of iron). into a baking furnace. The bakingfurnace may conveniently. be a silica Itube furnace and is graduallyheated during the baking operation by electricity or otherwise to atemperature of about 900 0., which temperature is maintained for about20 minutes. During this stage the baking furnace is filled with inertgas, preferably an atmosphere of dry hydrogen at a few millimetersabsolute pressure. The filaments after baking are conductive. They arethen subjected to a sintering operation, that is to say, an electriccurrent is passed through them in order to raise them to an intense at areduced pressure. Thus each filament .maybe sintered first for aboutthree seconds in an atmosphere of hydrogen at about (310 mm. pressureand again for'about one second in an atmosphere of hydrogen at about 110mm. pressure. Some filaments may require'a longer treatment withelectric current. After sintering the filaments are ready for mountingin lamps.

I In the case in which the filaments are rendered conductive andsintered in one operation, the process may be the same as abovedescribed up to the drying stage. The dried filaments are thenintroduced into an electric resistance furnace which convenientlyconsists of a vertical carbon tube through which a very heavy electriccurrent is passed. This tube is filled with an atmosphere of hydrogenfor example by leading hydrogen downward through it. The filaments aresuspended in the vertical tube and are raised to the temperaturenecessary to sinter them.

It is to be understood that the method of forming'and finishing thefilaments may be varied without departing from this invention. Forexample the filament as it is squirted may be passed directly into anapparatus in which it is subjected to the subsequent operations.'Further, the filaments may be cut into hairpin form or other suitableform at any stageof the manufacture or they may be kept in continuousform.

What I claim as my invention and desire to secure by Letters Patentis 1. The herein described process for the manufacture of tungstenfilaments for incandescent electric lamps which consists in intimatelymixing tungsten powder with a small proportion of sodium silicatesolution in the viscous form so as to produce a paste, squirting thesaid paste to form raw filaments and subjecting the raw filaments toheat so as to render them conductive and to cause them to sinter intofinished metallic tungsten filaments.

-. -2. The herein described process for the manufacture of tungstenfilaments for incandescent electric lamps which consists" in intimatelymixing tungsten powder with a small proportion of sodium silicatesolution in the viscous form so as to produce a paste, calcndcring themixture, squirting the said paste to form raw filaments, and subjectingthe raw filaments to heat so as to render them conductive and to causethem to sinter into finished metallic tungsten filaments.

3. The herein described process for the manufacture of tungstenfilaments for incandescent electric lamps which consists in intimatelymixing tungsten powder with a small proportion of sodium silicatesolution in the viscous form so as t produce a paste, calendering themixture, squirting the said paste to form raw filaments, drying therawfilaments and rendering the same conductive by baking, and thereaftersubjecting the baked filaments to a. high temperature in an inertatmosphere so as to sinter them into finished metallic tungstenfilaments.

4. The herein described process for the manufacture of tungstenfilaments for incandescent electric. lamps, whichconsists in intimatelymixing tungsten powder with a small proportion of sodium silicatesolution in the viscous form soas to produce a paste,

calenderingthe mixture, squirting the said paste to form raw filaments,drying the raw filaments, and subjecting them to heat in a suitableinert atmosphere inan electric furnace so as both to render thefilaments conductive and to sinter them in one operation.

5. The herein described step in the process for the manufacture oftungsten filaments for incandescent electric lamps by the squirtingprocess which consists in producing a squirtable paste by intimatelymixing tungsten powder with a small' proportion of a viscous solution ofsodium silicate.

6. The herein described composition of matter for use in the manufactureof tang sten filaments by the squirting process which consists of apaste composed of tungsten powder, and a small proportion of a viscoussolution of sodium silicate. f

In testimony whereof I have signed my name to this specification in thepresence of two subscribing witnesses.

JAMES ALEXANDER SCOULAR.

Witnesses:

E. J. WATT,

